Talk:Western Electric rules

Wikified as part of the Wikification wikiproject! JubalHarshaw 16:38, 2 November 2006 (UTC)

Rule 4: 8 or 9 points?

(Question below copied from Wikipedia Talk:WikiProject Statistics#Western Electric Rules. Qwfp (talk) 13:49, 3 July 2009 (UTC))

Rule 4 is stated as follows: "Nine consecutive points fall on the same side of the centerline (in zone C or beyond)"
I have a hunch that should be corrected to say, "Eight...". It seems like every web page I visit that mentions Western Electric rules, says that rule 4 is violated if just eight consecutive points fall on the same side of the centerline.--216.254.190.174 (talk) 13:09, 3 July 2009 (UTC)

This could be in the interpretation I think. Do you count the first point as part of the deviant set? The same problem occurs in some Nelson rules when you say that 4 points are constantly increasing, for example; what you have is a row of five points but only four on the constant increase. This seems clearer admittedly, but this might explain the difference you've spotted. Maybe someone thinks that they should only start a count of eight points once the second point is known.--GMcGlinn (talk) 23:42, 6 October 2009 (UTC

"Test: Zone C

Situation: Eight successive points on one side of the center line

Chance of false alarm: 7.8 per thousand"

This citation is from the book "SPC Essentials and Productivity Improvement: A Manufacturing Approach", Levinson, Tumbelty, ASQ Quality Press.

"7.8 per thousand" = 1/128 = 1/2⁷

From Statistcal Quality Control Handbook, 2nd edition, 10th printing May 1984, copyright 1956 Western Electric: on page 181 the rule (3)is clearly stated as "eight points in succession on one side of the centerline". The stated probability is 0.5^8 = 0.0039. Understanding how the probabilty is calculated leads one to udnerstand that the first point is incldued in the count of 8. The probability that any single point is above (or below) the centerline is 0.5. It then follows that the probabilty of two successive points on one side is 0.5 X 0.5 or 0.5^2. — Preceding unsigned comment added by Badaniels (talk • contribs) 19:33, 16 January 2012 (UTC)

I'm going to revert the "9" edit at https://en.wikipedia.org/w/index.php?title=Western_Electric_rules&oldid=960738412 to reflect the consensus that it should be 8. Zian (talk) 05:46, 15 June 2020 (UTC)

Chart Graphics

I've done the following

• Converted the image of four charts into SVG (original file:Western_electric_rules.gif). CONVERT
• Chopped the single image into four separate charts. CHOP
• Uploaded the four onto wikicommon. UPLOAD
• Put the four into the table that was already there. TABULATE
• Removed the original chart image. DELETE

DONE!--GMcGlinn (talk) 01:17, 7 October 2009 (UTC)